This invention relates to a fan assembly.
An important application of the fan assembly of the invention is extraction of air from a building space or from ducting. In a specific application, the fan assembly may be mounted in or on the roof of a building to extract air from the building space below or from ducting in the building. A known fan assembly which is currently used in such applications is the so-called “Whirlybird”, the main component of which is essentially a Savonius drag-type turbine. The turbine serves both to catch the wind and to extract air. Although fan assemblies of this type are in widespread use, they product a negligible pressure differential and are accordingly often unable to overcome the aerodynamic resistance to air flow through the space or ducting.